The manufacture of small diameter fiber reinforced metal matrix composites by any method except casting and liquid metal infiltration of wires requires uniformly spread fibers. Both nonconductive and conductive fibers have been spread mechanically, pneumatically and triboelectrically. Mechanical fiber spreaders, using physical contact, cause abrasion damage and breakage of small diameter brittle fibers and are thus not optimal in manufacturing the above composites. There are additional problems associated with nonconductive fibers. Nonconductive fibers tend to become electrically charged by rubbing with parts of the spreader or possibly by passing though the flow of gas in a pneumatic spreader. The phenomenon of charge transfer via moving contact is known as triboelectricity and is generally a hinderance in the spreading of nonconductive fibers mechanically or pneumatically. This charging results in the fibers being attracted to parts of the spreader; and often results in a malfunction of the spreader.
The process of transferring charge to fibers via a corona discharge effect has been used to spread nonconductive fibers. However, in these processes the fibers are commonly forwarded by pneumatic action or the direct application of tension to the fibers. Several patents have attempted to provide solutions to the above problems.
U.S. Pat. Nos. 4,081,856 and 3,967,118 (Sternberg) discloses the use of corona discharge in the spreading of fibers. The fibers are advanced by an air nozzle into a corona discharge region. The use of air to advance the fibers can result in non-uniform spreading and breaking of the fibers.
U.S. Pat. No. 3,456,156 (Kilby et al.) discloses an apparatus for applying an electrostatic charge to fibrous material. A fibrous web is passed through a corona discharge region and is electrically charged therein. The fibers are then deposited upon an oppositely charged moving belt to form a fiber mat. By depositing the fibers on an oppositely charged belt, there will be fibers that stick to the belt after the fiber mat is removed from the belt. This increases the amount of maintenance involved with this apparatus.
U.S. Pat. No. 4,999,733 (Kakuda) discloses an apparatus for reducing the static electricity on the surface of a web. This apparatus has a hollow roller which has holes through its outer surface. Located below these holes are electrodes used in creating a corona discharge. This corona discharge is used to remove electrostatic buildup on a web that is in contact with the roller.
Although all of the above-discussed apparatus relate to the spreading of fibers by corona discharge, they have the various disadvantages mentioned above.